I don't know about being any master of figuring it out, but, it all comes down to how popular an itinerary is. If a cruise is selling well then, it's not going to be on sale. Also as you noted, the previous price was better. It's a pretty common marketing tactic, increase the price, then put it on sale, but in many cases the sale price is higher than it was 6 months ago.
We tend to book in two scenarios, A. bucket list places that work into our schedule, generally you have to just bite the bullet and pay the going rate, B. bargain and sale cruises that also appeal to us.
Just keep watching for sales and checking prices. Every once and awhile a truly good deal comes along like the Extraordinary Savings sale last year.